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Re: Performance - moving from oracle to postgresql

From: "Radu-Adrian Popescu" <radu(dot)popescu(at)aldratech(dot)com>
To: "Greg Maples" <gregm(at)nimblefish(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Performance - moving from oracle to postgresql
Date: 2005-06-25 10:45:27
Message-ID: 41821.193.138.218.24.1119696327.squirrel@www.aldratech.com (view raw or flat)
Thread:
Lists: pgsql-performance
> "- Oracle has one particular performance enhancement that Postgres is
> missing.  If you do a select that returns 100,000 rows in a given order,
> and all you want are rows 99101 to 99200, then Oracle can do that very
> efficiently.  With Postgres, it has to read the first 99200 rows and
> then discard the first 99100.

When I was reading up on resultset pagination on AskTom I got a clear
impression that the same happens in Oracle as well.
Resultset is like:
0....START...STOP...END
0............STOP
     START...END
You first select all the rows from 0 to STOP and then from that select the
rows from START to end (which is now STOP). This is done using ROWNUM
twice and subselects.
It was discussed over there that this obviously produces higher response
times as you move towards the end of a very large resultset. Tom even
pointed out the same effect when using google search, as you move forward
through a very large (millions) search result.

Regards,
-- 
Radu-Adrian Popescu
CSA, DBA, Developer
Aldrapay MD
Aldratech Ltd.
+40213212243

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